scala type signature to allow numeric ops on members

Question

I have two case classes that are basically identical, except that one has Int and the other Double members. I'm trying to create a common trait that I can use for functions operating on either and allowing basic numeric operations. But so far i can't figure out how to use either the Numeric or Ops types:

trait Sentiment[A] {
  def positive: A
  def negative: A
}

case class IntSentiment(positive: Int, negative: Int) extends Sentiment[Int]

I would like to come up with a function constraint so that I can perform numeric ops on the members, something along the lines of:

def effective[A](sentiment: Sentiment[A]): A = {
  sentiment.positive - sentiment.negative
}

This does not work, and I figure i need to invoke the Numeric type class somehow, but the closest I've come is:

def effective[A](sentiment: Sentiment[A])(implicit num: Numeric[A]): A = {
  num.minus(sentiment.positive,sentiment.negative)
}

Is there a type constraint/signature on Sentiment and/or effective I can define to actually just use + and - ops on the members directly?

Incidentally, generic numerics in plain Scala are boxed, so aren't all that fast. You may not need them to be. If you do, check out Spire. — Rex Kerr, Nov 01 '14 at 21:17

score 6 · Accepted Answer · answered Nov 01 '14 at 20:28

6

import scala.Numeric.Implicits._

def effective[A : Numeric](sentiment: Sentiment[A]): A = {
  sentiment.positive - sentiment.negative
}

answered Nov 01 '14 at 20:28

Lee

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scala type signature to allow numeric ops on members

1 Answers1